1. Field of the Invention
The present invention relates to a method for treating blood plasma effective in treating autoimmune diseases, wherein a hollow fiber membrane which makes it possible to selectively remove immune complex, rheumatoid factors, etc., is employed.
2. Description of the Prior Art
Various methods of treating blood such as hemofiltration with filter membranes, hemoperfusion with adsorptive agents, etc., in addition to hemodialysis using dialysis membrane have been widely employed in a field of clinical medicine. Further, a technique which is called plasma-pheresis is being developed recently as a method for treating blood by extracorporeal circulation. In the plasmapheresis, blood is first separated into blood plasma components and blood cell components and the separated blood plasma components are treated in various methods in order to remove disease factors. More particularly, there are two methods of the plasmapheresis, one is a blood plasma substitution method in which blood plasma products made of blood plasma of other persons is substituted for the separated blood plasma component, and the other is a specific plasma component permeation method wherein the separated blood plasma component is further fractionated by a suitable method and then only specific fraction which induces problems is removed and other fractions are returned to the circulation in the body. As a therapeutic method, the blood plasma substitution method does not seem to be a preferable one, because, in the method, large amounts of blood plasma products are necessary as the whole amount of the plasma component of a patient is exchanged and therefore the method becomes expensive, and vicious influences may be brought as blood plasma products can not completely supplement each physiological substance in the plasma. Meanwhile, in the specific plasma component permeation blood, since only some parts of the blood plasma are removed and the other is taken back to the circulation in the body, the above mentioned problems of the former method are much improved. Thus, this method may be said to be a better therapeutic method.
There are already several studies and reports on such a specific plasma component permeation method as mentioned above. For example, there is a report on a method for treating the blood plasma using ethylenevinyl alcohol copolymer membrane (see Japanese Journal of Medical Instrumentation Vol. 49, Suppl. 259-261 (1979)). However, the ethylene-vinyl alcohol copolymer membrane disclosed therein inhibits permeation of 80 to 90% of dextran with a molecular weight of 100,000 as shown in FIG. 3 on page 261 of the Journal and has a water permeability of 20 to 34 ml/1.2 m.sup.2./hr.mmHg (about 17 to 28 ml/m.sup.2./hr.mmHg) which is considerably low.
On the other hand, a method wherein a membrane having micropores with average diameters of 0.05 to 0.20.mu. piercing through the membrane and distributed uniformly on its surface and having a water permeability at a very high level of 2 l/m.sup.2.hr.mmHg or more is used for filtering blood plasma is described in Japanese Patent Laid Open Nos. 75163/1981 and 751 64/1981. However, such a membrane having large pores has defects that it cannot efficiently filter and differentiate low-density lipoprotein (LDL) containing a large amount of cholesterol (molecular weight: 1,300,000 to 3,200,000), human blood plasma innumoglobulin M (molecular weight: about 950,000), and proteins with a molecular weight of some 2,000,000 or less which are not precipitated by cooling (immune complex or the like).